Solar Cell With High Aspect Ratio Gridlines Supported Between Co-Extruded Support Structures

ABSTRACT

A solar cell structure formed by extruding/dispensing materials on a substrate such that centrally disposed conductive high aspect ratio line structures (gridlines) are formed on the substrate surface with localized support structures coincidentally disposed on opposing side surfaces of the gridlines such that the gridlines are surrounded or otherwise supported by the localized support structures. In one embodiment the localized support structures are transparent, remain on the substrate after the co-extrusion process, and are covered by a layer of material. In another embodiment, the localized support structures are sacrificial support structures that are removed as part of the solar cell structure manufacturing process. In both cases the co-extrusion process is performed such that both the central gridline and the localized support structures are in direct contact with the surface of the substrate.

CROSS REFERENCE TO RELATED PATENTS AND APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/282,882 (Docket No. 20040932-US-NP) filed on Nov. 17, 2005 andentitled “EXTRUSION/DISPENSING SYSTEMS AND METHODS”, and is related toco-pending U.S. patent application Ser. No. 11/282,829 (Docket No.20040932Q-US-NP) filed on Nov. 17, 2005 and entitled“EXTRUSION/DISPENSING MULTIPLE MATERIALS TO FORM HIGH-ASPECT RATIOEXTRUDED STRUCTURES” (as amended).

BACKGROUND

The following generally relates to solar cells having gridlines formedby co-extrusion systems and methods. More particularly, it is directedto solar cells having gridlines formed by micro extrusion systems andmethods for co-extruding multiple similar and/or dissimilar materials toform relatively fine gridline structures with relatively high aspectratios. However, other applications are also contemplated herein.

With traditional extrusion a billet of material is pushed and/or drawnthrough a die to create a rod, rail, pipe, etc. Various applicationsleverage this capability. For instance, extrusion can be used with foodprocessing applications to create pasta, cereal, snacks, etc., pipepastry filling (e.g., meringue), pattern cookie dough on a cookie pan,generate pastry flowers and borders on cakes, etc. In anotherapplication, extrusion can be used with consumer goods, for example, tomerge different colored toothpastes together on a toothbrush.

However, conventional extrusion techniques are limited. For example,conventional techniques cannot render relatively high aspect-ratio(e.g., 10:1) fine featured (e.g., less then 5 micron) porous (e.g., 0.01mm RMS) structures for a cost below $1/sq. ft. Thus, extrusion typicallyis not used for creating conducting contacts and/or channels forelectrochemical (e.g., fuel), solar, and/or other types of cells, whichleverage high aspect-ratio fine featured porous structures to increaseefficiency and electrical power generation.

By way of example, with fuel cells high aspect-ratio fine featuredporous electrolyte structures provide a long reaction zone thatincreases utilization of the expensive catalyst needed for theelectrode. In addition, fuel cells can be complex structures since theyperform multiple functions including: conducting protons from themembrane to the reaction site; diffusing oxygen to the reaction sitewith a low partial pressure drop; conducting electrons from the porouselectrode to the reaction site; carrying heat away from the reactionsite; and withstanding a compressive mechanical load of about 100-200PSI. Conventional extrusion techniques cannot meet these demands at acost demanded by the fuel cell industry. In order to increaseefficiency, fuel cell manufacturers use more catalyst than desired toincrease the number of reaction sites and make agglomerates of carboncatalyzed with Platinum (Pt) in a matrix of porous, orpolytetrafluoroethylene (PTFE). With solar cells, high aspect-ratio finefeatured grid lines reduce the amount of shading, which allows morephotons to be captured, resulting in an increased electrical powergeneration. Conventional extrusion techniques are not able to producesuch grid lines at a cost demanded by the solar cell industry.

BRIEF DESCRIPTION

In one aspect, a solar cell structure is formed by extruding/dispensingmaterials on a substrate such that centrally disposed conductive highaspect ratio line structures (gridlines) are formed on the substratesurface with localized support structures coincidentally disposed onopposing side surfaces of the gridlines, and such that the gridlines aresurrounded or otherwise supported by the localized support structures.In one embodiment the localized support structures are transparent,remain on the substrate after the co-extrusion process, and are coveredby a layer of material. In another embodiment, the localized supportstructures are sacrificial support structures that are removed as partof the solar cell structure manufacturing process. In both cases theco-extrusion process is performed such that both the central gridlineand the localized support structures are in direct contact with thesurface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an extrusion device with an applicator forconcurrently applying one or more materials on a substrate;

FIG. 2 illustrates an exemplary applicator that can be with the deviceof FIG. 1;

FIG. 3 illustrates another exemplary applicator that can be used withthe device of FIG. 1;

FIG. 4 illustrates a plurality of dispensing ports associated with theapplicator described in FIG. 3;

FIG. 5 illustrates another exemplary configuration of an applicator thatcan be used the device of FIG. 1;

FIG. 6 illustrates an exemplary portion of a photovoltaic cell with gridlines created via the applicator of FIG. 1;

FIG. 7 illustrates a method for fabricating the photovoltaic celldescribed in FIG. 6;

FIG. 8 illustrates a method for fabricating grid lines of thephotovoltaic cell described in FIG. 6;

FIG. 9 illustrates an exploded view of a portion of an exemplaryapplicator for deposition of solar cell gridlines;

FIG. 10 illustrates a cross section of gridlines dispensed via theapplicator of FIG. 9;

FIG. 11 illustrates a portion of an exemplary applicator with verticallypositioned sub-channels for creating vertically layered entities;

FIG. 12 illustrates a cross section of gridlines dispensed via theapplicator of FIG. 11;

FIG. 13 illustrates an alternative configuration for producing avertically layered entity in which flows are vertically merged anddispensed;

FIG. 14 illustrates another alternative configuration for producing avertically layered entity in which flows are vertically merged togetherpair-wise;

FIG. 15 illustrates another alternative configurations for producingvertically layered entities in which flows are vertically mergedtogether external to the applicator;

FIG. 16 illustrates a portion of an exemplary fuel cell with at leastone channel created via the applicator described in FIG. 1;

FIG. 17 illustrates a method for fabricating the electrode of the fuelcell described in FIG. 13;

FIG. 18 illustrates a serial array of applicators;

FIG. 19 illustrates stacked applicators; and

FIG. 20 illustrates a matrix of applicators.

DETAILED DESCRIPTION

FIG. 1 illustrates an extrusion device 10 with an applicator 12 forconcurrently applying two or more substantially similar and/or differentmaterials (e.g., fluids, pastes, liquids, inks, etc.) on a substrate 14.The materials are applied through pushing and/or drawing techniques(e.g., hot and cold) in which the materials are pushed (e.g., squeezed,etc.) and/or drawn (e.g., via a vacuum, etc.) through the applicator 12and out one or more dispensing openings 16 of the applicator 12. Thematerials are dispensed to create one or more variously shaped entities(e.g., continuous, multi-sectional, rectangular, triangular, irregular,etc.) on the substrate 14. Suitable entities include, but are notlimited to, a bead, a point, a track, a pipe, a frame, a rail, a rod, aseal, a volume within a void, etc. The shape of the entity can bedefined through at least one of the shapes of the one or more dispensingopenings 16, the structure within the applicator 12 (e.g., channels),characteristics of the materials (e.g., viscosity, etc.), and theextrusion technique (e.g., flow rate, pressure, temperature, etc.).Suitable materials include, but are not limited to, silver, copper,aluminum, steel, plastic, ceramic, oil, etc., combinations thereof,and/or variations thereof, including combining the above with othersubstances to obtain a desired density, viscosity, texture, color, etc.

By way of example, multiple materials (e.g., with a viscosity from about1 centipoise (cP) to about several hundred thousand cP) can be pushedand/or pulled through the applicator 12 and dispensed together toproduce one or more structured layers of the materials on the substrate14. The multiple materials can be pushed and/or pulled through theapplicator 12 under laminar flow in order to mitigate mixing of thematerials. Mixing can be further reduced by using substantiallyimmiscible materials, including mixing a material with one or more othermaterials, impurities, dopants, coatings, etc. to create pastes, etc. Insome instances, the materials can be prepared such that they aremutually insoluble, enabling striped layers to be extruded onto thesubstrate 14 through the applicator 12 with relatively little mixing.The viscosities of the materials can also be matched to reduce shear andmixing between flows.

The applicator 12 can be a nozzle, a die, or any structure that receivesmaterials and facilitates applying the materials to the substrate 14.The applicator 12 can be micro-machined with structures that receive andconverge individual materials. For instance, the applicator 12 caninclude N channels, where N is an integer equal to or greater than one(e.g., thousands), for merging materials within the applicator 12 into asingle flow dispensed by the applicator 12. Each of the N channels canbe used for introducing a different material and/or multiple channelscan be used for introducing a substantially similar material. Where theapplicator 12 includes a single channel, the different material can beintroduced through similar and/or different ports into the channel.

Each channel can extend through a length (e.g., the entire length or asubset thereof) of the applicator 12. For instance, one or more of the Nchannels can be designed to be shorter than the length of the applicator12, but relatively longer than an entrance length in order to producelaminar flow, wherein flow velocity is stabilized prior to mergingmaterials. This can be achieved through known micro-machining techniquessuch as deep reactive ion etching, wafer bonding, etc. As brieflydiscussed above, creating the applicator 12 for laminar flow mitigatesand/or minimizes mixing of materials as the materials traverse throughthe applicator 12 and out of its opening. The N channels may also beshaped to counteract the effects of surface tension on the materials asthey progress from applicator 12 to the substrate 14. Each channel maybe uniquely and/or similarly shaped, including uniform and/ornon-uniform shapes.

To deposit the entity (e.g., bead, point, etc.) onto the substrate 14,the applicator 12 is suitably positioned with respect to the substrate14, and the one or more materials are dispensed through the applicator12. Such positioning can be based on factors such as distance betweenthe applicator 12 and the substrate 14, the angle of the dispensing endof the applicator 12 with respect to the substrate 14 (e.g., fromparallel to perpendicular to the substrate 14), etc. in order toincrease transfer efficiency, entity definition (e.g., width, height,length, diameter, etc), entity characteristics (e.g., strength,pliability, etc.), etc. In addition, such positioning may result incontact between the applicator 12 and the substrate 14. FIG. 1 depictsthe applicator 12 positioned above the substrate 14 during dispensing.

Prior to, during, and/or after dispensing the materials on the substrate14, the device 10 and the applicator 12 and/or the substrate 14 can bemoved. For example, to create a point (or dot, ball, etc.) at aparticular location on the substrate 14, the device 10 and applicator 12and/or the substrate 14 can be moved and suitably positioned.Subsequently, the materials can be dispensed to create the point.Thereafter, the device 10 and applicator 12 and/or the substrate 14 canbe moved to another position for a subsequent application, if any. Inanother example, to create a bead the device 10 and applicator 12 and/orthe substrate 14 can be moved to an initial position. During dispensingof the materials on the substrate 14, the device 10 and applicator 12and/or the substrate 14 can be moved in a suitable direction tofacilitate forming the bead on the substrate 14. FIG. 1 depicts theapplicator 12 dispensing a flow of materials to form a continuous beadon the substrate 14 as depicted at reference numeral 18.

To limit the tendency for the materials to intermix after extrusion, thebead of material leaving the applicator 12 can be quenched on thesubstrate 14 by making the substrate 14 relatively cold with respect tothe applicator 12. For example, a quenching component 15 can be used tocool the substrate 14. In another technique, the materials can be curedby thermal, optical and/or other means upon exit from the applicator 12.For example, a curing component 17 can thermally and/or optically curethe materials. If one or both materials includes an ultraviolet curingagent, the material can be bound up into solid form in order to enablefurther processing without mixing.

The applicator 12 can be manufactured a variety of ways. For instance,via deep silicon reactive ion etching and wafer bonding. In anotherinstance, the applicator 12 can be manufactured by electroplating metalup through features in a patterned resist structure. In anotherinstance, the applicator 12 can be manufactured by brazing togetherlayers of etched sheet metal. In yet another instance, the applicator 12can be manufactured by generating structures out of photo-definablepolymer such as SUB. In still another instance, the applicator 12 can bemachined or molded out of metal and/or plastic using conventionalmanufacturing techniques.

The relative speed of the motion between the applicator 12 and thesubstrate 14 and the speed at which the materials are dispenseddetermine characteristics such as whether the material is stretched orcompressed as it is placed on the substrate 14. These rates alsodetermine a thickness and/or an average thickness of the extrudedmaterial. Typically, these rates are set based at least in part on oneor more of the application, the materials, and/or the substrate 14. Forexample, these rates may be set to minimize separation between adjacentmaterials and/or deviations from desired dimensions. Airflow may be usedto direct one or more materials onto the substrate 14. For example,airflow around the dispensing opening of the applicator 12 can beprovided to pull the materials in desired directions. If the substrateis porous, as in the case of some fuel cell electrodes, airflow (e.g., avacuum) can be pulled through the substrate 14 to increase attachment ofthe material to the substrate 14. Flow can also be controlled throughcontrolling a pressure, temperature, etc. of the applicator 12 and/orthe substrate 14 to achieve the desired flow properties of the materialbeing extruded.

The duty cycle of each dispensed material can be controlled by adjustinga corresponding pressure of each material entering the applicator 12 inwhich each pressure can be similar and/or different. Additionally and/oralternatively, the duty cycle can be determined by the design of theapplicator 12. For instance, the pitch of each dispensed material can bedefined by a geometry of the applicator 12 (e.g., a width of theopening, a number of channels, shape of the channels, etc.). Both thepitch and the duty cycle can be configured for a particular design. Forexample, with one application the widths of the dispensed materials maybe substantially similar. With another application, a width of one ormore of the materials may be different. In yet another application, oneor more groups of channels may have different widths wherein thechannels within any one group may have substantially similar widths.Because surface tension forces may distort the pitch of the material(e.g., at the edges), the pitch of each channel can be adjusted tocompensate.

The one or more materials can be pre-filled within one or more storageelements (not shown) associated with the device 10. For instance, thematerials may be stored together in a similar storage element and/orseparated into individual storage elements. Additionally and/oralternatively, the materials may be supplied to the device 10 beforeand/or during extrusion via one or more optional input ports (not shown)of the device 10.

It is to be appreciated that the device 10 may include more than oneapplicator 12. Suitable configurations include, but are not limited to,a serial array of applicators 12 (e.g., staggered, adjacent, etc.), forexample to increase a width of a single pass; stacked applicators 12,for example to apply multiple layers in a single pass; a matrix ofapplicators (serial array/stacked combination) to concurrently increasethe width and the number of layers, for example to increase efficiency,etc. Examples of such configurations are depicted in FIGS. 18, 19, and20.

Each applicator 12 may be used to dispense a plurality of materials. Forinstance, substantially all of the applicators 12 could dispense similarmaterials. In another instance, the materials dispensed by one theapplicators 12 may be different from the materials dispensed by one ormore other applicators 12. In yet another example, each of theapplicators 12 could dispense different materials, wherein the materialsdispensed by any one applicator 12 may be similar and/or different. Instill another example, each of the applicators 12 may only dispense asingle material.

The multiple applicators 12 can be configured such that the device 10dispenses the materials in an interleaved and/or adjacent manner. Thus,a first applicator 12 dispensing K materials (where K is an integerequal to or greater than two) may dispense K adjacent materials, Kmaterials with gaps in between, and/or some combination thereof. Asecond applicator 12 dispensing L materials (where L is an integer equalto or greater than two) may dispense L adjacent materials next to the Kadjacent materials, L materials within the gaps between the K materials,and/or some combination thereof. A third, fourth, etc. applicator 12 canbe similarly used to apply materials in connection with the K and Lmaterials.

The device 10 can be used in connection with a variety of applications.For example, the device 10 can be used to create solar and/orelectrochemical (e.g., fuel, battery, etc.) cell electrodes. Forinstance, the device 10 can be used to extrude lines of the silver pasteinto a high aspect ratio grid lines surrounded by a sacrificial materialthat is in place only as long as it is needed to maintain the shape ofthe electrode on a solar cell substrate before or during any processingsuch as drying, curing, and/or sintering. A further advantage of thesacrificial material is that the added material leads to an overalllarger output orifice, and hence a lower pressure drop for a givenmaterial flow speed. Higher process speed is therefore achievable. Afurther advantage when convergent flow is used is that a minimumfabrication feature of the device 10 is larger than the minimum featureof an extruded gridline.

In addition to striped materials with a lateral variation, variations ofthe applicator 12 can be used to additionally and/or alternativelyintroduce materials with a vertical variation, for example, forintroducing barrier layers onto the substrate 14. Such verticalvariation can be implemented by forming channels that convergedissimilar materials together in the vertical direction within themanifold. For instance, with a solar cell application, it may beadvantageous to introduce a metal bi-layer onto the cell surface withone metal making contact to the silicon as a diffusion barrier, and asecond metal on top selected for either lower cost or higherconductance.

In another example, the device 10 can be used to facilitatemanufacturing light control films such as those used for computerprivacy screens. Typically, such screens have a series of tall, thinopaque louver layers in a clear matrix to limit the optical transmissionto a narrow range of angles. The applicator 12 could dispensealternating layers of opaque and clear materials to form a layer oflouvers by molding a ridge pattern into plastic and pressing a blackmatrix in between the ridges, wherein the two structures can belaminated together. In yet another example, the device 10 can be used toprint striated structures with a high aspect ratio such as artificialmuscle. For instance, lateral co-extrusion in combination with a valvingscheme could be used to make such structures. Multiple bands of musclelike material could be laid out in varied directions to produce avariety of actuations.

In another example, the device 10 and the applicator 12 can be used forprinting. For instance, by utilizing multi-pass printing, with orwithout registration, systems could be developed to create thickerlayers, or layers with a wider mix of materials, or functional compositematerials with novel properties. The process direction can also bechanged from layer to layer in order to create unique structures. Forexample, the device 10 and the applicator 12 could be used to createhigh strength plastics with crisscrossing grain structures similar toplywood. The device 10 and the applicator 12 enables printing a widerange of materials with viscosities up to the order several hundredthousand cP, with high aspect ratios on the order of 10:1 and featuresas small as 100 nanometers. Conventional jet printing technology islimited to materials with viscosities of about 40 cP and below and cannot make high aspect ratio features or features less than tens ofmicrons.

It is to be appreciated that employing the applicator 12 can reducecosts. For instance, typical costs associated with fabricatingelectrodes of a fuel cell can be reduced $10 to $20 per square foot ofelectrode area. Further, a wide array of materials ranging from paints,waxes, colloidal suspensions, pastes, resists, particle suspensions,gels, thixotropic materials, etc. can be extruded through the applicator12. The materials are not limited by the viscosity and/or by the need toform a vapor as with thermal inkjet, and more than one material can bedispensed simultaneously. The convergent applicator 12 can producefeature sizes with lateral dimensions on the order of 100 nanometers.The thickness of a layer (e.g., about 50 microns) can be variouslyapplied and since the materials typically are not ejected in a drop-wisefashion, large volumes of material can be printed in a single pass. Withconventional systems, drops of low viscosity liquid ejected from a printhead flatten out against a substrate, making low-aspect features. Theprinted mark would essentially become a 2D feature if the surface was toget wet. The applicator 12 can apply pastes to render three dimensional(3D) structures with relatively high aspect ratio, for example, 10:1 forfuel cell applications, which is virtually impossible with conventionalinkjet technology.

It will be appreciated that a productivity of a co-extrusion processtypically depends on the dispense rate of the fluids and that for afixed nozzle pressure, the dispense rate is lower for fluids of higherviscosity. In order to achieve a high process throughput, a lowviscosity is desired. On the other hand, in order to produce aco-extruded composite material with well defined interfaces and anoverall shape that follows the nozzle geometry, a high viscosity isdesired. One way to achieve high nozzle throughput and shape retentionis to dispense shear-thinning fluids. Such, non-Newtonian fluids,generally lower their viscosity in the presence of a shear stress,sometimes by large amounts, even by factors of 100 in some cases forexample as described in Rao et al., Adv. Materials vol. 17 no. 3 (2005).

FIG. 2 illustrates an exemplary applicator that can be used as theapplicator 12 of the device 10. It is to be appreciated that thisexample is provided for explanatory purposes and is not limiting; otherapplicator configurations and/or variations are also contemplated.

The applicator includes a manifold 20 having a first side 22 and asecond side 24. The manifold 20 can be fabricated by knownmicro-machining techniques such as deep reactive ion etching and waferbonding, for example. Each of the halves 22 and 24 can include Mchannels 26, wherein M is an integer equal to or greater than one (e.g.,thousands or more). For clarity and explanatory purposes, ten channelsare shown. The channels 26 typically are machined to extend a definedlength of the manifold 20. For instance, the channels 26 may befabricated to be relatively longer than an entrance length to createlaminar flow, but less then the entire length of the manifold 20, asillustrated. The channels 26 can also be machined to create similarand/or different shaped uniform and/or non-uniform channels.

The sides 22 and 24 are depicted as two independent structures; however,the manifold 20 can be created as a single unit and/or more than twopieces (e.g., each of the sides 22 and 24 may be formed from multiplecomponents). When the sides 22 and 24 are together, each of the channels26 forms one or more isolated compartments, conduits, passageways, etc.beginning at a first end 28 of the manifold 20 and extending toward asecond end 30 of the manifold 20 up to a region 32 where the channels 26terminate and converge into a single volume 34. In other instances, thecompartments, conduits, passageways, etc. formed by the channels 26 maynot be isolated such that materials flowing through adjacent channelsmay come into contact with each other.

The manifold 20 further includes ports for receiving materials. Asdepicted, a plurality of ports 36 can be interleaved and located on thefirst side 22, and a plurality of ports 38 can be interleaved andlocated on the second side 24. In other instances, the ports 36 and 38can all be located on one and/or both of the sides 22 and 24 of themanifold 20. In one instance, a single material may be fed into all ofthe ports 36 and 38. In another instance, a different material may befed into each of the ports 36 and 38. In yet another instance, one ormore materials may be fed into the ports 36 on the first side 22 of themanifold 20, and one or more different materials may be fed into theports 38 on the second side 24 of the manifold 20.

The different materials traverse through respective channels 26 andmerge within the region 34 of the manifold 20 to form a single flowcomprising multiple materials in which adjacent materials within theflow originate from adjacent channels and can be similar and/ordifferent materials. Under laminar flow conditions, the materialstraversing through the channels 26 and merging in the region 34typically do not mix or there is relatively minimal mixing of thematerials. As discussed previously, the viscosities of the materials canbe matched in order to reduce shear and mixing between the materials. Inaddition, the channels 26 may be shaped to counteract the effects ofsurface tension on a material as it progresses out of the manifold 20.

The manifold 20 and/or M channels 26 can be variously shaped tofacilitate producing laminar flow, merging different materials, and/orproducing a desired shape on the substrate 14. As depicted, a suitablemanifold shape includes a trapezoidal shape with channels extendingand/or tapering from the first end 28 of the manifold 20 to the secondend 30 of the manifold.

FIGS. 3 and 4 illustrate another exemplary applicator that can be usedas the applicator 12 of the device 10. Referring initially to FIG. 3,separate structures are used to dispense each material. As depicted, adispenser 40 is used to apply a first material, and a dispenser 42 isused to apply a Zth material, wherein Z is an integer equal to orgreater than one. The dispensers 40 and 42 can be positioned relative toeach other by micro-positioners and/or other suitable drives. Alignmentfrom channel-to-channel can also be achieved by interlocking featuresbuilt into the dispensers 40 and 42, such as comb-like structures. Sincethe materials come into contact outside of the dispensers 40 and 42, thematerials can be partially intermixable if the materials can be curedrelatively rapidly after being dispensed onto the substrate 14 (e.g.UV-curing). For instance, the materials can be co-mingled into a layerin flight between the channel tips and the substrate 14. Alternately,separate stripes on the substrate 14 may flow together once thematerials are deposited on the substrate 14.

FIG. 4 shows that each of the dispensers 40 and 42 can include one ormore dispensing ports. The dispenser ports 44 are used to apply thefirst material, and the dispenser ports 46 are used to apply the Zthmaterial. The ports 44 can be separated by a plurality of (equal ornon-equal) gaps 48 for applying a plurality of flows of first material.The ports 44 can be offset parallel to the ports 44 and separated by aplurality of (equal or non-equal) gaps 50 in order to facilitatedispensing the Zth material in the gaps 44 to render a flow comprisingalternating materials with a width based on an aggregate number of theports 44 and 46.

FIG. 5 illustrates another exemplary configuration of an applicator thatcan be used as the applicator 12. In this example, the applicator isused to apply two different materials on the substrate 14. Theapplicator includes the manifold 20, which, as described above, includesa plurality of channels 26 that are fabricated to facilitate creatinglaminar flow in order to merge materials received in each channel 26within the manifold 20 into a single flow of separate materials (withmaterial to material contact) while mitigating mixing of the materials.The channels 26 are associated with either the ports 36 or the ports 38,which are used to introduce at least one of the materials into themanifold 20. Two such ports are illustrated.

Typically, the two different materials are introduced into the manifold20 in an interleaved manner such that adjacent channels 26 are used fordifferent materials. However, similar materials can be introduced intoadjacent channels. As depicted, the two different materials can beintroduced into the manifold 20 from opposing sides 52 and 54. In otherconfigurations, the two different materials can be introduced from asubstantially similar side(s) (e.g., either the side 52 or the side 54),including introducing both materials from multiple sides (e.g., both theside 52 and the side 54). The side in which a material is introduced maybe arbitrary or defined in order to establish a particular sequence.

As illustrated, a first material is supplied to some of the channels 26of the manifold 20 through one or more of the plurality of ports 38, andanother material is supplied to different channels 26 of the manifold 20through the plurality of ports 36. It is to be appreciated the relativeposition of the ports 36 and 38 with respect to each other can bearbitrary such that the manifold 20 could be turned 180 degrees. Asdescribed above, the materials traverse (e.g., via a push, a pull, etc.technique) through corresponding channels and merge under laminar flowwithin the manifold 20 to form a single flow of materials.

The applicator further includes a housing 56, which reinforces theexterior of the applicator. The housing 56 can be designed to taper, ordiminish in size (e.g., thickness, diameter, width, etc.) from a backregion 58 to a front region 60. Such tapering provides relatively moresupport at the back region 58, which typically includes the highestpressure regions of the applicator, while enabling a dispensing end 62to be positioned adjacent to and/or in contact with the substrate 14.Such positioning can be based on factors such as distance between theapplicator and the substrate 14, the angle of the dispensing end 62 withrespect to the substrate 14, etc.

The applicator and/or the substrate 14 can be moved in order facilitateapplying the materials to the substrate 14. The relatively narrowerdispensing end 62 enables multiple applicators to be arrayed together ina staggered or non-staggered arrangement to increase a width of materialapplied with each pass of the applicators across the substrate 14. Thesubstrate 14 can be fed as cut sheets or in a roll-to-roll process. Theflow speed of the material can be controlled as described above. Forexample, the pressure of the materials can be suitably adjusted toeffectuate the flow speed.

FIG. 6 illustrates an exemplary portion of a photovoltaic cell, such asa solar cell, with grid lines created via the applicator 12. Thephotovoltaic cell includes a semiconductor 64 with a p-type region 66and an n-type region 68. One or both of the regions 66 and 68 of thesemiconductor 64 can be formed from semiconductor materials such as, forexample, Aluminium Arsenide, Aluminium Gallium Arsenide, Boron Nitride,Cadmium Sulfide, Cadmium Selenide, Diamond, Gallium Arsenide, GalliumNitride, Germanium, Indium Phosphide, Silicon, Silicon Carbide, SiliconGermanium, Silicon on insulator, Zinc Sulfide, Zinc Selenide, etc. Anelectric field is created across a p-n junction 70 and allows electronsand/or holes to flow from one region to another region of thesemiconductor 64, for example, upon the absorption of a photon.Electrons pass from the n-type region 68 into the p-type region 66, andholes pass from the p-type region 66 to the n-type region 68.

The photovoltaic cell further includes a contact 72 formed adjacent to aside 74 of the p-type region 66. The contact 72 can be formed via ametal paste such as an aluminum based paste. A grid contact 76 is formedadjacent to a side 78 of the n-type region 68. The grid contact 76includes conducting fingers 80 separated by non-conducting regions 82.The fingers 80 can be formed via a metal paste such as a silver basedpaste. The contacts 72 and/or 76 may be exposed to a heat treatment,and/or drying, curing, and/or sintering, and/or other processes.

After the contacts 72 and 76 are created, a plurality of the cells canbe interconnected in series and/or parallel, for example, via flat wiresor metal ribbons, and assembled into modules or panels. A sheet oftempered glass (not shown) may be layered over the grid contact 76and/or a polymer encapsulation (not shown) may be formed over thecontacts 72. The photon absorbing surface may include a textured surfaceand/or be coated with an antireflection material (e.g., silicon nitride,titanium dioxide, etc.) in order to increase the amount of lightabsorbed into the cell. In addition, the grid contract 76 can be formedas rectangular bars or variously shaped, for example, as triangularvolumes (e.g., with the point of the triangle facing away from thesemiconductor 64) that facilitate directing photons into thesemiconductor 64 and mitigating blocking photons from entering thesemiconductor 64, which can improve efficiency and/or generation ofelectrical power.

A electrode 84 can be connected to the grid contacts 76 and an externalload 86, and an electrode 88 can be connected to the external load 86and the contact 72. When photons 90 are absorbed into the semiconductor64, their energy excites electrons therein, which subsequently freelymove. Electrical current is generated when excited electrons in then-type region 68 travel through the grid contact 76 and the electrode 84to the external load 86 and back through the electrode 88 and thecontact 72 to the p-type region 72.

FIG. 7 illustrates a method for fabricating grid lines on a photovoltaicdevice such as the photovoltaic cell described in connection with FIG.6. At reference numeral 92, a semiconductor is formed. The semiconductorcan include various semiconductor materials as described above. Forinstance, the semiconductor can be formed by coupling a piece of n-typesilicon with a piece of p-type silicon to form a semiconductor p-njunction. In another instance, an n-type dopant (e.g., Phosphorus,Arsenic, Antimony, etc.) or a p-type dopant (e.g., Boron, etc.) isdiffused into a side of a silicon wafer. In yet another instance,naturally occurring semiconductors such as blue diamonds, which containBoron impurities, can be used. One or more of the photovoltaic cells canoptionally be coupled in a serial and/or parallel manner to create aphotovoltaic module or panel. At 94, a conducting contact is formedadjacent to the p-type region via known techniques. At 96, a conductinggrid is formed adjacent to the n-type region. In one example, the device10, as described above, is used to form the conducting grid. At 98,electrodes are coupled from the conducting contact and the conductinggrid to a load. When photons are absorbed into the semiconductor,electrical energy is generated via the photovoltaic effect.

FIG. 8 illustrates a method for fabricating the grid lines of thephotovoltaic device describe in connection with FIG. 6. At referencenumeral 100, one or more applicators (e.g., the applicators 12) can becoupled to an extruding device (e.g., the device 10). It is to beappreciated that the applicators can be coupled in a serial (e.g.,staggered or non-staggered) and/or parallel manner in order to increasethe width of each pass and/or concurrently apply multiple layers. At102, the device can be suitably positioned with respect to a surface ofthe photovoltaic substrate. Such positioning includes a distance betweendispensing ends of the applicators and the photovoltaic device, an angleof the dispensing ends of the applicators with respect to thephotovoltaic substrate, etc.

At 104, a silver paste and a sacrificial material (e.g., a material usedto maintain a shape of the electrodes) are fed into the applicators. Itis to be appreciated that the silver paste and sacrificial materials canbe pushed and/or drawn into the applicators through known techniques.Each of the applicators can include a plurality of channels fabricatedto facilitate producing laminar flow for merging materials within theapplicators while mitigating mixing of such materials. The silver pasteand the sacrificial material typically are fed in an interleaved mannersuch that adjacent channels are fed different materials (e.g., onechannel is fed silver paste while an adjacent channel is fed thesacrificial material), or alternating channels are fed a similarmaterial (e.g., every odd channel or every even channel is fed is eitherthe silver paste or the sacrificial material).

At 106, the materials traverse through their respective channels.Parameters such as rate, temperature, duty cycle, etc. are set based atleast in part on factors such as material viscosity and/or desiredcharacteristics such as grid line length, width, strength, resistance,etc. In addition, these parameters are set to produce a laminar flow foreach material traveling through each of the channels. At 108, aplurality of flows from the plurality of channels within each applicatoris merged into a single flow of alternating materials (e.g., silverpaste, sacrificial material, silver paste, sacrificial material, . . .or sacrificial material, silver paste, sacrificial material, silverpaste, . . . ). Since each flow is a laminar flow, the materials mergewith reduced mixing relative to non-laminar flows. The sacrificialmaterial is preferably, but is not limited to, a material with a closelymatched rheology to that of the silver paste.

At 110, the merged materials are dispensed from each of the applicatorsand applied to the photovoltaic substrate to create grid lines. It is tobe appreciated the device and applicators and/or the photovoltaicsubstrate can be moved relative to the other. The device can be usedmultiple times in order to create a desired width and/or apply a desirednumber of layers, for example, for introducing barrier layers onto thephotovoltaic substrate like a metal bi-layer with one metal makingcontact with the substrate as a diffusion barrier and another metalformed over it to reduce cost and/or increase conductance. The gridlines can be further processed, for example, via a heat treatment orsintering to make Ohmic contact with the substrate.

Using the applicator 12 for the grid lines results in grid lines with ahigh aspect ratio such as up to about 10:1 and relatively fine featuressuch as less than about 5 to 10 microns. Conventional solar cellproducing systems are not able to produce grid lines with such aspectratios and feature size. With conventional systems, the grid lines coverabout 4% of the area and are opaque and metallic and, thus, blockphotons from entering the semiconductor 64. The high aspect ratio finefeature grid lines produced via the applicator 12 take up less than 4%of the area and allow more photons to enter the semiconductor 64, whichimproves electrical power output. A further advantage arises becausenarrow grid lines have a smaller metal-to-semiconductor contact area,which has the beneficial effect of reducing electron-hole recombination.

FIG. 9 illustrates an exploded view of a portion of aco-extrusion/dispense applicator suitable for the deposition of solarcell gridlines. The applicator includes an array of outlets 112. Each ofthe outlets 112 corresponds to a single gridline and dispenses amaterial composite consisting of a central metal line of high aspectratio with supporting material adjacent to one or more sides of themetal line. FIG. 10 depicts a cross section of two such gridlinesdispensed via the applicator of FIG. 9 on a substrate 120. Each of thedispensed gridlines includes a metal line 116 and support material 118.Returning to FIG. 9, a convergent path 120 leading to each outlet 112has advantages in comparison to a straight channel. For example, theextruded features can be finer than the finest minimum design feature ofthe applicator itself. In addition, the applicator uses less material tosupport the gridline compared to one that uses a single outlet.

By way of example, a co-extrusion applicator with the estimatedparameters illustrated in Table 1 could be used to dispense thematerials to make gridlines on a crystalline silicon solar cell.

TABLE 1 Exemplary applicator parameters for generating a gridline. SheetThickness 152 microns Gridline Pitch 2.5 mm Applicator Speed 1 cm/secPast Viscosity 100,000 Cp Applicator Angle 45 degrees Applicator ExitWidth 304.8 Microns Silver Width 49.2 Microns Silver Line Cross Section7,500 microns{circumflex over ( )}2 Silver Line Aspect Ratio 3.10:1Silver Flow 0.075 mm{circumflex over ( )}3/sec Applicator Compression6.2:1 Applicator Pressure Drop 2.24 atm

With this design, convergent channels are patterned into a sheet ofmaterial with a thickness of approximately 0.15 mm. The output orificesof the applicator/nozzles are repeated on a pitch of 2.5 mm. At anapplicator/nozzle pressure of approximately 2.24 atmospheres, paste of1000 poise is ejected at a rate of 1 cm/sec. The central stripe ofsilver is approximately 50 microns wide with an aspect ratio of 3.1.

It will be appreciated that an applicator/nozzle with many separateoutputs may have an inherent instability, particularly when the fluidbeing dispensed undergoes large amounts of shear thinning. Thisinstability could cause fluids in different channels to divide intodifferent flow states. For example, the flows could divide into a lowflow, low shear, high viscosity state in some channels while others havea high flow, high shear, low viscosity state. A particularly undesirablecondition is one in which for a given fluid displacement rate, theoverall pressure drop is lowest for a combination of high and low outputflows. One way to avoid uneven flows from a dispense nozzle withmultiple outputs (such as the applicator of FIG. 9) is to drive eachoutput from a separate fluid pump. A particularly desirable and costeffective way to achieve this is to create an array of positivedisplacement pumps in which fluid in multiple reservoirs issimultaneously compressed by a single actuator, such as a motor and leadscrew driving a plate with multiple plungers.

A further refinement of the arrayed lateral co-extrusion devicedescribed above in FIG. 9 includes the addition of manifolds directed atthe introduction of vertically layered laminar flows of materials. FIG.11 illustrates such an applicator in which a channel includes two ormore sub-channels 122 positioned vertically with respect to each otherto generate a vertically layered entity 124 via an exit port outlet 126.Each of the sub-channels includes an inlet 128 for introducing amaterial. The applicator can include a plurality of the channels with asimilar and/or different number of sub-channels 122 to concurrently formhorizontal and vertical layers. The foregoing structure facilitateslowering the metallization cost of solar cells. By way of example, asshown in FIG. 12, the vertically layered entity 124 includes acomparatively expensive contact material 130 such as a silver gridlinemetallization is formed adjacent to the substrate 132. A layer such as anickel metallization that acts as a diffusion barrier 134 is formedvertically adjacent to the contact material 130. Vertically layered overthe diffusion barrier 134 is a metal line 136 such as a layer of coppermetallization that serves as an additional low cost material to carrycurrent generated by the solar cell. A support material 138 is formedhorizontally adjacent to the contact material 130, the diffusion barrier134, and/or the metal line 136.

FIGS. 13 and 14 illustrate various vertical co-extrusion/dispenseconfigurations. In FIG. 13, the vertical flows through the sub-channels122 can be simply merged together and dispensed at the outlet 126 asshown. Alternatively, the sub-channels 122 can converge together inorder to produce finer features and to lessen to the total pressure dropfor a given flow rate. For example, in FIG. 14, one layer of a stack ofbonded plates is shown. On this layer, flows through the sub-channels122 converge vertically. Layers above and below may contain fillingorifices. Additional layers above and below can be introduced and mergethe laterally disposed flows of sacrificial material.

An alternate device and method for producing a multilayer stack ofdispensed metals on a substrate is illustrated in FIG. 15. In thisdevice, individual layers from the outlets 126 are combined external tothe dispense head in such a fashion that as the substrate moves relativeto the dispense head, layers of dispensed paste lay on top of oneanother. This device has the potential advantage of producing lessmixing.

FIG. 16 illustrates an exemplary fuel cell anode with at least onechannel created via the applicator of FIG. 9. It is to be appreciatedthat the applicator of FIG. 9 can be used to create barrier channelsand/or electrodes for other electrochemical devices such a batteries(e.g., zinc-air), etc.

The fuel cell anode includes a porous electrode and gas diffusion layer144, a membrane 146 consisting of for example phosphoric acid bound in apolymer structure, and composite porous electrode 148 disposed therebetween. The electrode 144 typically is a porous electrode and gasdiffusion layer which allows reactants, such as oxygen for a hydrogenfuel cell, to permeate into the composite porous electrode 148. Thecomposite porous electrode 148 consists of alternating vertical stripesof nanoporous hydrophobic material (e.g., polytetrafluoroethyleneparticles) 150 and nanoporous hydrophobic conductor and catalyst 152(e.g., graphite particles and platinum). A catalyst, such as platinum,in the conductor lines 152 catalyzes the reaction to produce water. Inone instance, the reaction is characterized by the following:

The porous nature of the stripes 150 and 152 provide for continuousreplenishment of the reactants consumed within the composite porouselectrode 148.

Relatively high aspect ratio (10:1) thin feature (5-10 microns) porouslines are desirable because they produce a long reaction zone thatincreases utilization of the expensive catalyst needed for theelectrode. However, conventional extrusion techniques cannot fabricatesuch lines on relatively rough (0.01 mm RMS) substrates at costs below$1/square foot. In addition, the structure should facilitate conductingprotons form the membrane to the reaction site, diffusing oxygen to thereaction site with low partial pressure drop, conducting electrons fromthe porous electrode to the reaction site, carry heat away from thereaction site, and withstand a compressive mechanical load of 100-200PSI. The challenges imposed by the electrode structure and its targetcost place nearly impossible demands on conventional photolithographic,direct marking, and molding techniques. To compensate for thisdeficiency, conventional techniques commonly use more catalyst thandesired to increase the number of reaction sites and/or employagglomerates of carbon catalyzed with Platinum in a matrix of a porousmaterial, or polytetrafluoroethylene (PTFE). The applicator of FIG. 9can be used to produce high aspect-ratio (10:1) thin conductor lines 150interleaved with porous PTFE 152 (5 microns or less) on relatively rough(0.01 mm RMS) substrates at costs below $1/square foot.

FIG. 17 illustrates a method for fabricating the membrane electrodeassembly of the fuel cell described in FIG. 16. At 154, suitablyposition a device employing the applicator of FIG. 9 with respect to asurface of a substrate. Such positioning includes a distance betweendispensing ends of the applicators and the photovoltaic device, an angleof the dispensing ends of the applicators with respect to thephotovoltaic substrate, etc. It is to be appreciated that more than oneof the applicators can be concurrently used. In addition, the one ormore applicators can be coupled in a serial (e.g., staggered ornon-staggered) and/or parallel manner in order to increase the width ofeach pass and/or concurrently apply multiple layers.

At 156, a first material for creating the hydrophilic lines, and asecond material for creating the hydrophobic lines are fed into theapplicator(s). Each of the applicators can include a plurality ofchannels fabricated to facilitate producing laminar flow for mergingmaterials within the applicators while mitigating mixing of suchmaterials. The first and second materials typically are fed in aninterleaved manner such that adjacent channels are fed differentmaterials, or alternating channels are fed a similar material.Parameters such as rate, temperature, duty cycle, etc. are set based atleast in part on factors such as material viscosity and/or desiredcharacteristics such as grid line length, width, strength, resistance,etc. In addition, these parameters are set to produce a laminar flow foreach material traveling through each of the channels.

At 158, a plurality of flows from a plurality of channels within eachapplicator is merged into a single flow of alternating materials (e.g.,first material, second material, first material, second material, . . .or second material, first material, second material, second material, .. . ). Since each flow is a laminar flow, the materials merge withreduced mixing relative to non-laminar flow flows. At 160, the mergedmaterials are dispensed from the applicator(s) to create a plurality ofchannels the form the electrolyte. It is to be appreciated that theapplicator(s) and/or substrate can be moved relative to the other. Theapplicator(s) can be used multiple times in order to create a desiredwidth and/or apply a desired number of layers.

To further reduce the mixing of pastes and the particles that thematerials include, the materials can be formulated such that they aresubstantially immiscible. The particles that form the network of porousmedia in the electrode can be coated, if necessary, with hydrophilic orhydrophobic coatings to affect their intermixing. For instance, bothpairs and combinations of liquids and colloidal suspensions can be madeto be mutually insoluble, enabling striped layers of these materials tobe extruded onto the substrate through the applicator withoutsubstantial mixing.

Table 2 provides examples of throughput related parameters for theapplicators described herein. It is to be understood that these examplesare provided for illustrative purposes and are not limiting. Thethroughput related parameters were obtained by estimating a pressuregradient to produce a Poiseuille flow in a rectangular cross section atvarious points along a length of the applicator 12.

TABLE 2 Throughput related parameters for the applicators describedherein. Ejector Convergence 10 to 1 Injector Pitch 50 microns InjectorSize 25 microns Array Width 1000 injectors Number of applicators 10nozzles Applicator Height 200 microns Page Print Time 1 minutes Pagesize 300 mm Layer Thickness 50 microns Exit Pitch 5 microns Array width50 mm at input Applicator width 5 mm at output Applicator speed 30mm/sec Applicator flow speed 7.5 mm/sec Applicator flow rate 7.5mm{circumflex over ( )}3/sec Viscosity 5000 cP or 5 kg/m.sec Flow Rate7.5 mm{circumflex over ( )}3/sec or 7.5E−09 m{circumflex over ( )}3/secApplicator length 50 mm Pressure Drop 24 PSI

From Table 2, for a modest number of applicators, for example, about 10,and a pressure of about 24 PSI, a relatively highly viscous materialcould be printed at a rate of about 1 square foot per minute. Theinjector pitch at the wide end of the applicator is about 50 microns,and the width converges from about 50 mm to about 5 mm, with about 1000injection ports, and a printed pitch at the applicator opening of about5 microns. The height of the layer deposited by the applicator is about50 microns, whereas the applicator channel is about 200 microns deep.The deposited layer is thinned by stretching, or moving the substratefaster (e.g., about four-times) than the flow rate of the materials asthey leave the applicator. Depending on the properties of the materials,it may be possible to stretch a bead by relatively large ratios. Forexample, if the applicator channel is about 500 microns deep, and thelayer thickness is about 50 microns, a substantially similar print speedcan be achieved with a pressure drop of only about 1.7 PSI. For finerpitch, the applicator can include more injection ports or a narroweropening.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intoother similar and/or different systems or applications. Also, unforeseenor unanticipated alternatives, modifications, variations or improvementstherein, which are also intended to be encompassed by the followingclaims, may be made by those skilled in the art.

1. A solar cell structure, comprising: a substrate; at least onegridline formed on the substrate; separate localized transparent supportstructures that surround each of the at least one gridline; and a layerformed over the resultant separate localized transparent supportstructures and the substrate.
 2. The solar cell structure of claim 1,wherein the at least one gridline has an aspect ratio greater than 2:1.3. The solar cell structure of claim 1, wherein the at least onegridline has a width in the range of 100 nanometers to 100 microns. 4.The solar cell structure of claim 1, wherein the separate localizedtransparent support structures comprise a material that is disposedhorizontally adjacent to said each at least one gridline such that thematerial contacts opposing side edges of said each at least onegridline.
 5. The solar cell structure of claim 1, wherein both the atleast one gridline and the material forming the separate localizedtransparent support structures are in direct contact with a surface ofthe substrate.
 6. The solar cell structure of claim 1, wherein the atleast one gridline comprises a silver paste.
 7. The solar cell structureof claim 1, wherein the least one gridline covers less than 4% of asurface area of said substrate.
 8. An intermediate structure comprising:a substrate; and a plurality of parallel gridlines Rutted on thesubstrate, wherein each of the plurality of parallel gridlines includes:a central high aspect ratio line structure formed by a first material;and a sacrificial support structure formed by a second material, whereinthe second material is disposed in contact with the first material suchthat side portions of the sacrificial support structure contact opposingside edges of the central high aspect ratio line structure.
 9. Theintermediate structure of claim 8, wherein the central high aspect ratioline structure of each of the plurality of parallel gridlines has anaspect ratio greater than 2:1.
 10. The intermediate structure of claim8, wherein the central high aspect ratio line structure of each of theplurality of parallel gridlines has a width in the range of 100nanometers to 100 microns.
 11. The intermediate structure of claim 8,wherein both the central high aspect ratio line structure and thesacrificial support structure of each of the plurality of parallelgridlines are in direct contact with a surface of the substrate.
 12. Theintermediate structure of claim 8, wherein the central high aspect ratioline structure of each of the plurality of parallel gridlines comprisesa silver paste.
 13. The intermediate structure of claim 12, wherein thesacrificial support structure of each of the plurality of parallelgridlines comprises a material having a closely matched rheology to thatof the silver paste.
 14. The solar cell structure of claim 8, whereinthe central high aspect ratio line structure of all of the plurality ofparallel gridlines cover less than 4% of a surface area of saidsubstrate.
 15. An intermediate structure comprising: a substrate havinga surface; and an elongated composite structure disposed on the surfaceof the substrate, the composite structure including: a central linestructure formed by a first co-extruded material, and a supportstructure formed by a second co-extruded material that is disposed onthe central structure such that side portions of the support structureare disposed horizontally adjacent to the central structure withoutsubstantial intermixing of the first and second materials, wherein boththe side portions of the support structure and the central structure arein direct contact with the surface of the substrate.
 16. Theintermediate structure of claim 15, wherein the central line structurehas an aspect ratio greater than 2:1.
 17. The intermediate structure ofclaim 15, wherein the central line structure has a width in the range of100 nanometers to 100 microns.
 18. The intermediate structure of claim15, wherein the central line structure comprises a silver paste.
 19. Theintermediate structure of claim 18, wherein the second materialcomprises a material having a closely matched rheology to that of thesilver paste.
 20. The intermediate structure of claim 15, wherein thecentral line structure cover less than 4% of a surface area of saidsubstrate.